The present invention relates to an organic (electro-)luminescence device and particularly to an organic luminescence device for emitting light by applying an electric field to a film of an organic compound (organic compound layer).
An organic luminescence device generally comprises a pair of electrodes (comprising an anode and cathode) and a film comprising a fluorescent organic compound. Into the organic compound layer (film), holes and electrons are injected from the anode and the cathode, respectively, thus forming excitons of the fluorescent organic compound. When the excitons are returned to ground state, the organic luminescence device emits light or causes luminescence.
According to study by Eastman Kodak Co. (xe2x80x9cAppl. Phys. Lett.xe2x80x9d, vol. 51, pp. 913- (1987)), it has been reported that a function-separation type organic luminescence layer comprising a layer of an aluminum quinolinol complex (as electron transporting and luminescent material) and a layer of a triphenylamine derivative (as hole transporting material) causes luminescence at a luminance (brightness) of ca. 1,000 cd/m2 under application of a voltage of 10 volts. Examples of related U.S. Patents may include U.S. Pat. Nos. 4,539,507; 4,720,432 and 4,885,211.
Further, by changing species of the fluorescent organic compound, it is possible to effect luminescence in a broad wavelength region ranging from ultraviolet region to infrared region. In this regard, various compounds have been extensively studied in recent years. Such compounds has been proposed in, e.g., U.S. Pat. Nos. 5,151,629: 5,409,783 and 5,382,477, and Japanese Laid-Open Patent Applications (JP-A) Nos. 2-247278, 3-255190, 5-202356, 9-202878 and 9-227576.
In addition to the above-mentioned organic luminescence device using a conjugated polymer has been reported by a research group of Cambridge University (xe2x80x9cNaturexe2x80x9d, vol. 347, pp. 539- (1990)). According to this report, a layer of polyphenylenevinylene (PPV) is formed through wet-coating process and luminescence by the use of single layer is confirmed. Such an organic luminescence device using a conjugated polymer has also been proposed by, e.g., U.S. Pat. Nos. 5,247,190; 5,514,878 and 5,672,678, and JP-A Nos. 4-145192 and 5-247460.
As described above, recent progress in organic luminescence device is noticeable and allows luminescent devices with high luminescence (brightness), various (light-)emission wavelengths, high-speed responsiveness, small thickness and light weight under application of lower voltage, thus suggesting possibility of wide applications.
However, the above-described organic luminescence devices are still required to effect light output (emission) at a higher luminance and/or a higher conversion efficiency in the present state. These organic luminescence devices are also still insufficient in terms of durability such that the devices are liable to be changed in their properties with time when used for a long period or liable to be deteriorated by the influence of ambient air containing oxygen or of humidity. Further, in the case of using the organic luminescence devices for full-color display, it is necessary to effect light emission of blue, green and red with good color purity. However, such light emission has not been realized satisfactorily.
As an electron injecting material, oxadiazole derivatives (e.g., JP-A 2-216791 and JP-A 4-363891) or triazine derivatives (e.g., JP-A 7-41759 and JP-A 7-90260) have been proposed. However, organic luminescence devices using such compounds are not sufficient in stability of film and electron injection efficiency, thus resulting in lower luminance (of emitted light) and the shorter life of the device.
A generic object of the present invention is to provide improvements to problems are mentioned above encountered in organic luminescence devices proposed heretofore.
A more specific object of the present invention is to provide an organic (electro-) luminescence device capable of effecting light output (emission) at high efficiency and luminance while realizing the prolonged life.
Another object of the present invention is to provide an organic luminescence device capable of providing a wide variety of emission wavelengths and emission hues and a good durability.
A further object of the present invention is to provide an organic luminescence device which can easily be prepared relatively inexpensively.
According to the present invention, there is provided an organic luminescence device, comprising: a pair of electrodes comprising an anode and a cathode, and an organic compound layer disposed between the pair of electrodes, wherein the organic compound layer comprises a compound represented by the following formula (I): 
wherein R1 to R6 independently denote a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted heterocyclic group, with the proviso that each pair of R1 and R2, R3 and R4, an R5 and R6 or of R1 and R6, R2 and R3, and R4 and R5 may be connected to each other to form a fused ring structure.
By using the organic compound represented by the above-mentioned formula (1) in the organic luminescence device, it becomes possible to effect luminescence at a very high luminance under application of a lower voltage and provide an excellent durability.
Particularly, the organic compound layer comprising the compound of the formula (1) used in the present invention is useful as an electron injection layer.
Further, the resultant organic compound layer can be can be prepared through vacuum deposition, casting, wet-coating, etc., thus readily realizing a larger size thereof relatively inexpensively.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.